In both immunization- and natural infection-driven immune responses, dendritic cells (DCs) play a critical role in initiating T cell activation, as they are the only cells known to have the capacity to prime naIve T cells in vivo. It is poorly understood how the trafficking of dendritic cells is controlled by the immunization site microenvironment, and whether or not this process can be optimized for subunit or DNA vaccines. Given the uncertainty in our understanding and the intrinsic complexity of the DC life cycle during an immune response, we would like to dissect this process through controlled release of factors that allow selective manipulation of DC trafficking. We hypothesize that vaccines which control the dynamics of dendritic cells entering, patrolling and leaving the vaccination site will have a significant impact on both the number and state of DCs reaching the lymph nodes for subsequent T cell activation, and thus on resulting immune responses. To test this hypothesis, we would like to determine the immunological consequence of modulating DC migration into and out of the immunization site quantitatively. To do this, we have devised a set of tools that enables us to modulate each step in DC trafficking precisely in vivo. Our model immunization system is comprised of two components that can be co-injected as a vaccine: microspheres that release factors which modulate DC trafficking with controlled rates, and hydrogel nanoparticles that deliver antigen and immobilized maturation factors in concert. Using this system, we will analyze the number and state of DCs at the injection site and the draining lymph node and the number and state of cognate T cells in the draining lymph node as a function of time. We will examine the effect of 1) modulating DC and DC precursor attraction to the immunization site and 2) modulating DC emigration from the immunization site to draining lymph nodes. DC trafficking will be quantitatively manipulated by immunizing with microspheres that release DC chemoattractants or modulating factors such as prostaglandins with defined release kinetics and total doses. Such studies are expected to advance our understanding of dendritic cell function, catalyze the development of more advanced materials for control of immune responses, allow the construction of a mathematical model to describe dendritic cell dynamics, and enable more rational design of vaccines.